Operators are used after their operands for example to add 3 and 4, instead of writing 3 + 4 which is infix expression, postfix expression will be 3 4 +. The order of evaluation of operators is always left-to-right, and brackets cannot be used to change this order. Postfix expression of example above will be A B C + * D /. Operators act on values immediately to the left of them. This is also called as Polish postfix notation or simply postfix notation.

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Prefix Notation (Polish Notation):

Example: +A B

Operators are used before their operands for example to add 3 and 4, instead of writing 3 + 4 which is infix expression, prefix expression will be + 3 4. The expressions given above are equivalent to / * A + B C D . Operators are evaluated left to right. Operators act on the two nearest values on the right. Also known as normal Polish notation, Polish prefix notation or simply prefix notation

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